bug#353: M-x customize lacks search function

[jidanni]

The screen that greets the user upon M-x customize should have a
Search [________]
box. E.g., the user is looking for things that match cursor.*color,
and finds some using M-x apropos, but would like to find where inside
all the menus he should go now here to get to the M-x customize
specific ones.

Also good would be a standard BACK key.

http://www.useit.com/alertbox/application-mistakes.html
http://www.useit.com/alertbox/designer-user-differences.html